Allergy

17 August 2011

High-efficiency particulate arresting (HEPA) filter

A high-efficiency particulate arresting (HEPA) filter is a type of air filter. Air filters remove microscopic particles, such as bacteria, dust mites, and animal dander from the air. HEPA filters are often used to purify the air in the home or in healthcare facilities to help prevent the spread of infections, diseases, and/or allergies.

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BACKGROUND

A high-efficiency particulate arresting (HEPA) filter is a type of air filter. Air filters remove microscopic particles, such as bacteria, dust mites, and animal dander from the air. HEPA filters are often used to purify the air in the home or in healthcare facilities to help prevent the spread of infections, diseases, and/or allergies.

A HEPA filter can remove more than 99% of indoor airborne particles that are 0.3 micrometers wide. This includes allergens such as dust mites, pollen, animal dander, and mold, as well as bacteria. Particles of this size, also called the most penetrating particle size (MPPS), are the most difficult to filter. Particles that are the MPPS are the least likely to become trapped in the filter's fibers when they enter the HEPA filter. The HEPA is able to filter particles that are larger and smaller than 0.3 micrometers with even greater efficiency.

The first HEPA filter, which was designed in the 1940s, was used by the U.S. Atomic Energy Commission during the Manhattan Project to prevent airborne, radioactive contaminants from spreading. The filter was later marketed to consumers in the 1950s to reduce airborne allergens, pollutants, and disease-causing microorganisms (like bacteria and viruses). The term HEPA became a registered trademark and a generic term for high-efficiency particulate arresting filters.

Over the years, HEPA filters have evolved to meet the needs of consumers. They are used to help prevent the spread of airborne bacteria, fungi, and viruses, which can potentially lead to infections. They also reduce the number of airborne pollutants (like tobacco smoke) and allergens (like dust mites and animal dander) that can lead to infection, disease, and/or allergies.

HEPA filters are available in a wide variety of sizes. Larger rooms require filters that are able to purify a greater volume of air. Some can filter 600 cubic feet of air per minute (cfm), while others can filter 1,200cfm or 2,000cfm. Consumers should check with the manufacturers of specific HEPA filters to determine the optimum size for their homes. HEPA filters are sold at department stores, hardware stores, and many home furnishing stores. They can also be purchased online

HEPA filters are also commonly used in combination with high-energy ultraviolet lights in healthcare facilities and nursing homes. The ultraviolet light kills the bacteria and viruses that become trapped in the filter. In this way, air around the patients is cleaner, and they are less likely to become sick.

USES

Air purifier: High-efficiency particulate arresting (HEPA) air purifiers are used to filter the air that is circulating indoors. They help remove microscopic particles, such as bacteria, dust mites, and animal dander from the air. A fan forces air through the filter. The more times the air flows through the filter, the cleaner the room. These air purifiers do not remove odors, gasses, or chemicals. HEPA filters can also be installed in air conditioning units and heating ducts in the home or in healthcare facilities.

Vacuum: Many vacuum cleaners also have built-in HEPA filters to remove particles from the exhaust air. This can be beneficial for individuals who have indoor allergies, asthma, or weakened immune systems. The filter traps the tiny particles called allergens, such as dust mites, pet dander, fungi, and pollen, as well as disease causing microorganisms, such as bacteria and mold. However, in order for a HEPA filter in a vacuum to be effective, the vacuum must be designed to have all of the air enter the filter, with none of it leaking past it. Also, vacuum cleaners with HEPA filters must have more powerful motors in order to overcome the extra air resistance of the filter, while still providing enough cleaning power.

Hospitals: Since HEPA filters can effectively remove airborne particles that can cause infection, disease, and/or allergies, they are often used in healthcare facilities and nursing homes. According to the U.S. Centers for Disease Control and Prevention (CDC), HEPA filters can help clean air before it is circulated to areas of a healthcare facility, including airborne infection isolation rooms (patient-care room where environmental factors are controlled to prevent infection). HEPA air purifiers are commonly used in combination with high-energy ultraviolet lights in healthcare settings. The ultraviolet light kills the bacteria and viruses that become trapped in the filter.

MICROCON© is the only patented mobile hospital air purification system in the United States. The mobile air purification system is a high-capacity air purifier that is specifically designed to remove airborne pathogens (disease-causing organisms), such as Mycobacterium tuberculosis, which causes tuberculosis.

FUNCTION

High-efficiency particulate arresting (HEPA) filters are made of many intertwined fibers. Particles become trapped in these fibers by one of three ways: interception, impaction, or diffusion.

As air is pushed through the filter, the particles that come extremely close to a fiber (within one radius of a fiber) will stick to that fiber. This is called interception.

Larger particles cannot avoid the fibers. These particles become embedded in the fibers when the air is pushed through the filter. This process is called impaction.

The smallest airborne particles, especially those smaller than 0.1 micrometer wide (like microscopic bacteria), become trapped in the fibers in a process called diffusion. Tiny air particles are constantly colliding with gas molecules in the air. These small air particles continue to collide with gas molecules once they enter the filter. When the particles crash into gas molecules, the force of contact will cause the particles to either stick to or embed in the fibers.

AUTHOR INFORMATION

This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

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Copyright © 2011 Natural Standard (www.naturalstandard.com)
 

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Dr Morris is the Principal Allergist at the Cape Town and Johannesburg Allergy Clinics with postgraduate diplomas in Allergology, Dermatology, Paediatrics and Family Medicine dealing with both adult and childhood allergies.

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